Such wiping systems are known per se in the prior art. For example, U.S. Pat. No. 4,236,450, the content of which is incorporated by reference in the present application, describes an installation for the continuous cleaning of a wiping roller of an intaglio printing machine. The disclosed installation consists of a wiping system comprising a tank onto which the wiping roller is rotatably mounted, this tank enclosing various cleaning members in contact with the periphery of the wiping roller for cleaning the surface of the wiping roller under the action of a cleaning liquid (commonly designated as “wiping solution”). The cleaning members comprise several brushes and scraper blades which are distributed at regular intervals along the periphery of the wiping roller. More specifically, the wiping system comprises, at an upstream location with respect to the direction of rotation of the wiping roller, a first row of spray nozzles extending parallel to the axis of the wiping roller for spraying wiping solution against the surface of the wiping roller and a first scraper blade which removes approximately 95% of the mass of ink adhering to the surface of the wiping roller. Downstream of the first row of spray nozzles and of the first scraper blade, there is arranged a series of rows of spray nozzles distributed along the periphery of the wiping roller, these rows of nozzles being each combined with brushes. Lastly, another scraper blade (which is commonly designated as “drying blade”) is disposed in contact with the surface of the wiping roller and makes it possible to eliminate wiping solution residues remaining on the surface of the wiping roller. An additional row of spray nozzles can be mounted behind the first scraper blade so as to prevent ink particles from accumulating behind this scraper blade. The spray nozzles are connected to the outlet of a pump which supplies them with clean wiping solution. The scraper blades, spray nozzles and brushes are mechanically supported in the tank, the position thereof being adjustable. More specifically, the position of the first scraper blade can be adjusted by means of a hydraulic-actuated control arm enabling the first scraper blade to be retracted away from the surface of the wiping roller or to adjust its pressure against the wiping roller. On the other hand, the brushes and associated rows of spray nozzles are mounted on a common pair of curved rails which are guided in the tank between guide rollers, so that the whole brushes-spray-nozzles assembly can rotate concentrically with the axis of rotation of the wiping roller.
Another ink wiping device for intaglio rotary printing machines is known from U.S. Pat. No. 4,499,825, the content of which is incorporated by reference in the present application. The disclosed system comprises a tank containing wiping solution in which is immersed the wiping roller as well as a cleaning assembly for cleaning the circumferential surface of the wiping roller. The cleaning assembly includes, along the direction of rotation of the wiping roller, at least one brush unit adjustably supported in the tank and having a plurality of rows of bristles having distal ends located in the vicinity of the circumferential surface of the wiping roller. In addition, each brush unit includes a cleaning sheet made of synthetic-fibered non-woven cloth supported on the brush unit and interposed between the circumferential surface of the wiping roller and the distal ends of the bristles. Accordingly, ink that has been removed and transferred from the printing plate to the ink wiping roller is wiped off the latter by the cleaning sheet pressed against the ink wiping roller under the resiliency of the bristles and is dissolved in the cleaning solution. Since the roller and the cleaning assembly (i.e. brush units) are immersed in the cleaning solution, it is necessary to use a drying blade (made of hard rubber as indicated in this patent) for scraping off the cleaning liquid from the ink wiping roller. Below this drying blade, that is upstream of the blade with respect to the direction of rotation of the wiping roller, there is an additional pad of synthetic fibered non-woven cloth supported on a holder above the surface of the wiping solution for blocking off the wiping solution which tends to be carried by the wiping roller as it rotates. The design taught by this patent is disadvantageous in that the cleaning assembly and the wiping roller are immersed in the wiping solution, which thus requires a substantial amount of wiping solution inside the tank. Further, since the wiping roller is partly immersed in the wiping solution; the cleaning efficiency of such a cleaning installation tends to be rather low because the wiping roller is always in contact with wiping solution that is contaminated with ink components. As a matter of fact, the cleaning efficiency is directly dependent on the efficiency of the non-immersed cleaning pad to clean the surface of the wiping roller.
Another system is disclosed in the European Patent application published under the number EP 0 514 756, the content of which is incorporated by reference in the present application. This application teaches a wiping apparatus for an intaglio printing press comprising a cleaning assembly including a series of cleaning members each consisting of a base arranged parallel to the axis of rotation of the wiping roller which carries an arched sheet pad made of a strip of carbon tool steel, said sheet pad having a multitude of tiny openings for scraping ink and being in elastic contact with the peripheral surface of the wiping roller. In addition, a brush unit is further provided downstream of the arched cleaning members, bristles of the brush unit being in elastic contact with the surface of the wiping roller. Accordingly, the ink transferred by the wiping operation from the intaglio printing plates to the wiping roller is scraped through said multitude of tiny openings made in the sheet pads and is dissolved in the cleaning solution, the surface of the wiping roller being lastly cleaned by the brush unit. According to this prior art solution, the lower part of the wiping roller can be immersed in the wiping solution, together with the cleaning members (in a way similar to the solution of U.S. Pat. No. 4,499,825 mentioned above) or wiping solution can be sprayed against the surface of the wiping roller (in a way similar to the solution of U.S. Pat. No. 4,236,450 mentioned above). A major disadvantage of the solution taught in EP 0 514 756 resides in the fact that the surface of the wiping roller is in direct contact with the highly resistant arched sheet pads made of carbon tool steel. As compared to the other solutions using either brushes or soft cleaning sheets/pads, this causes extensive wear of the comparatively softer surface of the wiping roller (which wiping roller is typically coated with a polymer compound such as PVC) which in turn degrades the cleaning efficiency of the wiping apparatus and requires frequent renewal of the wiping roller's coating. In the worst case, the contact of the wiping roller with such highly resistant material can even cause considerable damage to the wiping roller's outer surface.
Japanese utility model 07-015339 U, the content of which is incorporated by reference in the present application, discloses a wiping equipment which wipes off the excess of ink of a wiping roller in an intaglio printing machine which follows a similar route as that taught in EP 0 514 756. The difference resides in that, according to JP 07-015339 U, a large cleaning sheet of carbon tool steel is used in lieu of the various arched cleaning members, the cleaning sheet being in contact with the surface of the wiping roller over a substantially greater portion. As with the solution of EP 0 514 756, the cleaning sheet comprises a multitude of tiny openings to remove the ink present on the surface of the roller. A major drawback of this solution again resides in the fact that the cleaning sheet is made of hard material and is in direct contact with the surface of the wiping roller, which solution leads to the above-described problems. This drawback is even more pronounced in this latter case as the contact surface between the wiping roller and the carbon tool steel cleaning sheet is substantially larger than in the solution disclosed in EP 0 514 756.
U.S. Pat. No. 6,341,556, the content of which is incorporated by reference in the present application, discloses another wiping device of an intaglio printing press which uses a wiping roll cleaning sheet mounted on a base member. The wiping roll cleaning sheet is formed of three superimposed sheets each having through holes, namely a supporting sheet supported by the base member, a cleaning sheet in contact with the circumferential surface of the roller, and a pressing sheet interposed between the cleaning sheet and the supporting sheet for pressing the cleaning sheet against the surface of the wiping roller. As described, the supporting sheet and the cleaning sheets are both preferably constructed as wire nets made of stainless steel, while the pressing sheet is made of an unwoven fabric of synthetic resin (such as nylon). In a specific embodiment, the cleaning sheet can be made of a plate of steel instead of a wire net, said plate having many small holes formed therein and being similar to the plates known from Japanese utility model JP 07-015339 U cited above. The disclosed wiping device further includes, disposed downstream of the above-mentioned wiping roll cleaning sheet with respect to the direction of rotation of the wiping roller, a second wiping unit comprising a cleaning sheet made of an unwoven fabric (for example of synthetic resin) which is supported on top of a number of brushes as taught for example in U.S. Pat. No. 4,499,825 cited hereinabove. Accordingly, in this prior art, the teaching is to use a metallic plate or wire net in direct contact with the wiping roller to remove the ink and wiping solution in addition to a fabric sheet mounted over brushes.
Other similar systems are in addition known from U.S. Pat. Nos. 5,765,480 and 4,899,654, both related to wiping devices for intaglio printing machines.
Another solution is disclosed in Japanese patent application No. JP 2000-202984. This document describes an ink wiping system comprising a first cleaning member for applying clean wiping solution in a laminar stream state against the surface of the wiping roller and a downstream-located cleaning assembly comprising a perforated metallic supporting member conforming to a part of the circumferential surface of the wiping roller, which supporting member supports a porous cleaning sheet contacting the surface of the wiping roller. This cleaning assembly further comprises its own spray means in the form of spraying nozzles which spray wiping solution against the surface of the wiping roller through the supporting member and the cleaning sheet. One disadvantage of this solution resides in the fact that the cleaning efficiency of the first cleaning member is limited because most of the wiping solution applied by this first cleaning member will fall back in the wiping tank and will not be appropriately exploited. As a consequence, the downstream-located cleaning assembly has to be provided with its own spraying means for spraying wiping solution against the surface of the wiping roller. In addition, the efficiency of this latter cleaning assembly is also limited as the sprayed wiping solution first has to penetrate through the cleaning sheet before reaching the surface of the wiping roller. An improved solution is thus still required.
A problem encountered in the known installations spraying wiping solution is the fact that the nozzles, which have a small diameter, may be blocked or obturated by particles present in the cleaning solution so that the cleaning effect is reduced. In such case, it becomes necessary to stop the printing machine, remove the wiping roller to gain access to the shafts with the nozzles and to remove said shafts from the machine to be able to clean the nozzles in a remote place. Once this has been done, the shafts must be assembled and adjusted in the machine and then only can the wiping roller be brought back in position.
The same drawback is present in the systems using plates with a multitude of tiny holes such as described above. The holes may be blocked or obturated by particles hence reducing the efficiency of the plate, this problem being even worse in immersed systems. As mentioned here above, it is then necessary to stop the printing machine and carry out cleaning operations.
The same problem also arises with the solution of JP 2000-202984 where the cleaning assembly is provided with nozzles that will also have a tendency to be blocked by particles.
All these operations are time consuming and, since the machine is not working anymore, they have an important cost.